docs: def txn_useNonce(self, server_url, timestamp, salt):
          """Return whether this nonce is present, and if it is, then
          remove it from the set.
  
          str -> bool"""
          if abs(timestamp - time.time()) > nonce.SKEW:
              return False
  
          try:
              self.db_add_nonce(server_url, timestamp, salt)
          except self.exceptions.IntegrityError:
              # The key uniqueness check failed
              return False
          else:
              # The nonce was successfully added
              return True